Computed Tomography (CT) scanning of patient anatomy is used by radiologists for medical diagnosis. In CT scanning of a patient, a 3D (or volume) image is generated by means of an X-ray source which is rapidly rotated around the patient. A large quantity of images is obtained resulting in slices of the scanned area, which is electronically reassembled to constitute a 3D image of the scanned area. The CT scanning is a measurement of the amount of X-rays absorbed in the specific volume elements constituting the 3D image, and each volume element represents the density of the tissue comprised in the volume element.
The CT image is a 3D counterpart to the traditional 2D X-ray image. In order to obtain a 2D X-ray image, an X-ray source is mounted in a fixed position, and a patient is located and oriented in-between the X-ray source and a detecting screen. In this method a projection of the tissue density along the ray path is acquired.
If a medical diagnosis on the background of CT scanning necessitate surgery, a surgeon nearly always requests medical images in the operating theater that display the particular medical problem. In some instances, the original CT data of interest is printed to film, in the form of cross-sectional slices through the patient anatomy and these films are provided to the surgeon. In many other instances, however, the patient is sent to an X-ray facility for acquiring 2D X-ray images in addition to the CT images. The request for X-ray images is accompanied with a precisely specified patient position for the X-ray imaging procedure. Such 2D X-ray projection images are often requested by the surgeons because the slice images from CT data are frequently considered as not providing sufficient information, or the number of slice images is too large for use in an operation situation. Sending a patient to an X-ray facility for obtaining X-ray images is expensive, it takes time and it exposes the patient to additional X-ray radiation.
Furthermore, the positioning of a patient in an X-ray apparatus to obtain an optimal X-ray image is a skill that technicians must learn. Training is often done on-the-job, which sometimes requires re-acquiring X-ray images when the original images do not show the anatomy of interest in the correct way. Obtaining optimal X-ray images may be difficult due to organs shadowing the area of interest as well as a proper and precise positioning of the X-ray source and the detector plate.
To avoid exposing dental students to X-ray radiation during training of obtaining X-ray images of teeth, Umea University has built a virtual training system. The virtual training system comprises a tooth model acquired from a CT scanning. An X-ray image plate may be positioned and the virtual model may be oriented, and an X-ray image of the teeth is simulated.